grep searches for PATTERN in each FILE. A FILE of “-” stands for
standard input. If no FILE is given, recursive searches examine the
working directory, and nonrecursive searches read standard input. By
default, grep prints the matching lines.
In addition, the variant programs egrep and fgrep are the same as
grep -E and grep -F, respectively. These variants are deprecated,
but are provided for backward compatibility.

Generic Program Information--help Output a usage message and exit.
-V, --version
Output the version number of grep and exit.
Matcher Selection-E, --extended-regexp
Interpret PATTERN as an extended regular expression (ERE, see
below).
-F, --fixed-strings
Interpret PATTERN as a list of fixed strings (instead of
regular expressions), separated by newlines, any of which is
to be matched.
-G, --basic-regexp
Interpret PATTERN as a basic regular expression (BRE, see
below). This is the default.
-P, --perl-regexp
Interpret the pattern as a Perl-compatible regular expression
(PCRE). This is experimental and grep -P may warn of
unimplemented features.
Matching Control-e PATTERN, --regexp=PATTERN
Use PATTERN as the pattern. If this option is used multiple
times or is combined with the -f (--file) option, search for
all patterns given. This option can be used to protect a
pattern beginning with “-”.
-f FILE, --file=FILE
Obtain patterns from FILE, one per line. If this option is
used multiple times or is combined with the -e (--regexp)
option, search for all patterns given. The empty file
contains zero patterns, and therefore matches nothing.
-i, --ignore-case
Ignore case distinctions, so that characters that differ only
in case match each other.
-v, --invert-match
Invert the sense of matching, to select non-matching lines.
-w, --word-regexp
Select only those lines containing matches that form whole
words. The test is that the matching substring must either be
at the beginning of the line, or preceded by a non-word
constituent character. Similarly, it must be either at the
end of the line or followed by a non-word constituent
character. Word-constituent characters are letters, digits,
and the underscore. This option has no effect if -x is also
specified.
-x, --line-regexp
Select only those matches that exactly match the whole line.
For a regular expression pattern, this is like parenthesizing
the pattern and then surrounding it with ^ and $.
-y Obsolete synonym for -i.
General Output Control-c, --count
Suppress normal output; instead print a count of matching
lines for each input file. With the -v, --invert-match option
(see below), count non-matching lines.
--color[=WHEN], --colour[=WHEN]
Surround the matched (non-empty) strings, matching lines,
context lines, file names, line numbers, byte offsets, and
separators (for fields and groups of context lines) with
escape sequences to display them in color on the terminal.
The colors are defined by the environment variable
GREP_COLORS. The deprecated environment variable GREP_COLOR
is still supported, but its setting does not have priority.
WHEN is never, always, or auto.
-L, --files-without-match
Suppress normal output; instead print the name of each input
file from which no output would normally have been printed.
The scanning will stop on the first match.
-l, --files-with-matches
Suppress normal output; instead print the name of each input
file from which output would normally have been printed. The
scanning will stop on the first match.
-m NUM, --max-count=NUM
Stop reading a file after NUM matching lines. If the input is
standard input from a regular file, and NUM matching lines are
output, grep ensures that the standard input is positioned to
just after the last matching line before exiting, regardless
of the presence of trailing context lines. This enables a
calling process to resume a search. When grep stops after NUM
matching lines, it outputs any trailing context lines. When
the -c or --count option is also used, grep does not output a
count greater than NUM. When the -v or --invert-match option
is also used, grep stops after outputting NUM non-matching
lines.
-o, --only-matching
Print only the matched (non-empty) parts of a matching line,
with each such part on a separate output line.
-q, --quiet, --silent
Quiet; do not write anything to standard output. Exit
immediately with zero status if any match is found, even if an
error was detected. Also see the -s or --no-messages option.
-s, --no-messages
Suppress error messages about nonexistent or unreadable files.
Output Line Prefix Control-b, --byte-offset
Print the 0-based byte offset within the input file before
each line of output. If -o (--only-matching) is specified,
print the offset of the matching part itself.
-H, --with-filename
Print the file name for each match. This is the default when
there is more than one file to search.
-h, --no-filename
Suppress the prefixing of file names on output. This is the
default when there is only one file (or only standard input)
to search.
--label=LABEL
Display input actually coming from standard input as input
coming from file LABEL. This is especially useful when
implementing tools like zgrep, e.g., gzip -cd foo.gz | grep--label=foo -H something. See also the -H option.
-n, --line-number
Prefix each line of output with the 1-based line number within
its input file.
-T, --initial-tab
Make sure that the first character of actual line content lies
on a tab stop, so that the alignment of tabs looks normal.
This is useful with options that prefix their output to the
actual content: -H,-n, and -b. In order to improve the
probability that lines from a single file will all start at
the same column, this also causes the line number and byte
offset (if present) to be printed in a minimum size field
width.
-u, --unix-byte-offsets
Report Unix-style byte offsets. This switch causes grep to
report byte offsets as if the file were a Unix-style text
file, i.e., with CR characters stripped off. This will
produce results identical to running grep on a Unix machine.
This option has no effect unless -b option is also used; it
has no effect on platforms other than MS-DOS and MS-Windows.
-Z, --null
Output a zero byte (the ASCII NUL character) instead of the
character that normally follows a file name. For example,
grep -lZ outputs a zero byte after each file name instead of
the usual newline. This option makes the output unambiguous,
even in the presence of file names containing unusual
characters like newlines. This option can be used with
commands like find -print0, perl -0, sort -z, and xargs -0 to
process arbitrary file names, even those that contain newline
characters.
Context Line Control-A NUM, --after-context=NUM
Print NUM lines of trailing context after matching lines.
Places a line containing a group separator (--) between
contiguous groups of matches. With the -o or --only-matching
option, this has no effect and a warning is given.
-B NUM, --before-context=NUM
Print NUM lines of leading context before matching lines.
Places a line containing a group separator (--) between
contiguous groups of matches. With the -o or --only-matching
option, this has no effect and a warning is given.
-C NUM, -NUM, --context=NUM
Print NUM lines of output context. Places a line containing a
group separator (--) between contiguous groups of matches.
With the -o or --only-matching option, this has no effect and
a warning is given.
File and Directory Selection-a, --text
Process a binary file as if it were text; this is equivalent
to the --binary-files=text option.
--binary-files=TYPE
If a file's data or metadata indicate that the file contains
binary data, assume that the file is of type TYPE. Non-text
bytes indicate binary data; these are either output bytes that
are improperly encoded for the current locale, or null input
bytes when the -z option is not given.
By default, TYPE is binary, and when grep discovers that a
file is binary it suppresses any further output, and instead
outputs either a one-line message saying that a binary file
matches, or no message if there is no match.
If TYPE is without-match, when grep discovers that a file is
binary it assumes that the rest of the file does not match;
this is equivalent to the -I option.
If TYPE is text, grep processes a binary file as if it were
text; this is equivalent to the -a option.
When type is binary, grep may treat non-text bytes as line
terminators even without the -z option. This means choosing
binary versus text can affect whether a pattern matches a
file. For example, when type is binary the pattern q$ might
match q immediately followed by a null byte, even though this
is not matched when type is text. Conversely, when type is
binary the pattern . (period) might not match a null byte.
Warning: The -a option might output binary garbage, which can
have nasty side effects if the output is a terminal and if the
terminal driver interprets some of it as commands. On the
other hand, when reading files whose text encodings are
unknown, it can be helpful to use -a or to set LC_ALL='C' in
the environment, in order to find more matches even if the
matches are unsafe for direct display.
-D ACTION, --devices=ACTION
If an input file is a device, FIFO or socket, use ACTION to
process it. By default, ACTION is read, which means that
devices are read just as if they were ordinary files. If
ACTION is skip, devices are silently skipped.
-d ACTION, --directories=ACTION
If an input file is a directory, use ACTION to process it. By
default, ACTION is read, i.e., read directories just as if
they were ordinary files. If ACTION is skip, silently skip
directories. If ACTION is recurse, read all files under each
directory, recursively, following symbolic links only if they
are on the command line. This is equivalent to the -r option.
--exclude=GLOB
Skip any command-line file with a name suffix that matches the
pattern GLOB, using wildcard matching; a name suffix is either
the whole name, or any suffix starting after a / and before a
+non-/. When searching recursively, skip any subfile whose
base name matches GLOB; the base name is the part after the
last /. A pattern can use *, ?, and [...] as wildcards, and
\ to quote a wildcard or backslash character literally.
--exclude-from=FILE
Skip files whose base name matches any of the file-name globs
read from FILE (using wildcard matching as described under
--exclude).
--exclude-dir=GLOB
Skip any command-line directory with a name suffix that
matches the pattern GLOB. When searching recursively, skip
any subdirectory whose base name matches GLOB. Ignore any
redundant trailing slashes in GLOB.
-I Process a binary file as if it did not contain matching data;
this is equivalent to the --binary-files=without-match option.
--include=GLOB
Search only files whose base name matches GLOB (using wildcard
matching as described under --exclude).
-r, --recursive
Read all files under each directory, recursively, following
symbolic links only if they are on the command line. Note
that if no file operand is given, grep searches the working
directory. This is equivalent to the -d recurse option.
-R, --dereference-recursive
Read all files under each directory, recursively. Follow all
symbolic links, unlike -r.
Other Options--line-buffered
Use line buffering on output. This can cause a performance
penalty.
-U, --binary
Treat the file(s) as binary. By default, under MS-DOS and MS-
Windows, grep guesses whether a file is text or binary as
described for the --binary-files option. If grep decides the
file is a text file, it strips the CR characters from the
original file contents (to make regular expressions with ^ and
$ work correctly). Specifying -U overrules this guesswork,
causing all files to be read and passed to the matching
mechanism verbatim; if the file is a text file with CR/LF
pairs at the end of each line, this will cause some regular
expressions to fail. This option has no effect on platforms
other than MS-DOS and MS-Windows.
-z, --null-data
Treat input and output data as sequences of lines, each
terminated by a zero byte (the ASCII NUL character) instead of
a newline. Like the -Z or --null option, this option can be
used with commands like sort -z to process arbitrary file
names.

A regular expression is a pattern that describes a set of strings.
Regular expressions are constructed analogously to arithmetic
expressions, by using various operators to combine smaller
expressions.
grep understands three different versions of regular expression
syntax: “basic” (BRE), “extended” (ERE) and “perl” (PCRE). In GNU
grep there is no difference in available functionality between basic
and extended syntaxes. In other implementations, basic regular
expressions are less powerful. The following description applies to
extended regular expressions; differences for basic regular
expressions are summarized afterwards. Perl-compatible regular
expressions give additional functionality, and are documented in
pcresyntax(3) and pcrepattern(3), but work only if PCRE is available
in the system.
The fundamental building blocks are the regular expressions that
match a single character. Most characters, including all letters and
digits, are regular expressions that match themselves. Any meta-
character with special meaning may be quoted by preceding it with a
backslash.
The period . matches any single character.
Character Classes and Bracket Expressions
A bracket expression is a list of characters enclosed by [ and ]. It
matches any single character in that list; if the first character of
the list is the caret ^ then it matches any character not in the
list. For example, the regular expression [0123456789] matches any
single digit.
Within a bracket expression, a range expression consists of two
characters separated by a hyphen. It matches any single character
that sorts between the two characters, inclusive, using the locale's
collating sequence and character set. For example, in the default C
locale, [a-d] is equivalent to [abcd]. Many locales sort characters
in dictionary order, and in these locales [a-d] is typically not
equivalent to [abcd]; it might be equivalent to [aBbCcDd], for
example. To obtain the traditional interpretation of bracket
expressions, you can use the C locale by setting the LC_ALL
environment variable to the value C.
Finally, certain named classes of characters are predefined within
bracket expressions, as follows. Their names are self explanatory,
and they are [:alnum:], [:alpha:], [:cntrl:], [:digit:], [:graph:],
[:lower:], [:print:], [:punct:], [:space:], [:upper:], and
[:xdigit:]. For example, [[:alnum:]] means the character class of
numbers and letters in the current locale. In the C locale and ASCII
character set encoding, this is the same as [0-9A-Za-z]. (Note that
the brackets in these class names are part of the symbolic names, and
must be included in addition to the brackets delimiting the bracket
expression.) Most meta-characters lose their special meaning inside
bracket expressions. To include a literal ] place it first in the
list. Similarly, to include a literal ^ place it anywhere but first.
Finally, to include a literal - place it last.
Anchoring
The caret ^ and the dollar sign $ are meta-characters that
respectively match the empty string at the beginning and end of a
line.
The Backslash Character and Special Expressions
The symbols \< and \> respectively match the empty string at the
beginning and end of a word. The symbol \b matches the empty string
at the edge of a word, and \B matches the empty string provided it's
not at the edge of a word. The symbol \w is a synonym for
[_[:alnum:]] and \W is a synonym for [^_[:alnum:]].
Repetition
A regular expression may be followed by one of several repetition
operators:
? The preceding item is optional and matched at most once.
* The preceding item will be matched zero or more times.
+ The preceding item will be matched one or more times.
{n} The preceding item is matched exactly n times.
{n,} The preceding item is matched n or more times.
{,m} The preceding item is matched at most m times. This is a GNU
extension.
{n,m} The preceding item is matched at least n times, but not more
than m times.
Concatenation
Two regular expressions may be concatenated; the resulting regular
expression matches any string formed by concatenating two substrings
that respectively match the concatenated expressions.
Alternation
Two regular expressions may be joined by the infix operator |; the
resulting regular expression matches any string matching either
alternate expression.
Precedence
Repetition takes precedence over concatenation, which in turn takes
precedence over alternation. A whole expression may be enclosed in
parentheses to override these precedence rules and form a
subexpression.
Back References and Subexpressions
The back-reference \n, where n is a single digit, matches the
substring previously matched by the nth parenthesized subexpression
of the regular expression.
Basic vs Extended Regular Expressions
In basic regular expressions the meta-characters ?, +, {, |, (, and )
lose their special meaning; instead use the backslashed versions \?,
\+, \{, \|, \(, and \).

The behavior of grep is affected by the following environment
variables.
The locale for category LC_foo is specified by examining the three
environment variables LC_ALL, LC_foo, LANG, in that order. The first
of these variables that is set specifies the locale. For example, if
LC_ALL is not set, but LC_MESSAGES is set to pt_BR, then the
Brazilian Portuguese locale is used for the LC_MESSAGES category.
The C locale is used if none of these environment variables are set,
if the locale catalog is not installed, or if grep was not compiled
with national language support (NLS). The shell command locale -a
lists locales that are currently available.
GREP_OPTIONS
This variable specifies default options to be placed in front
of any explicit options. As this causes problems when writing
portable scripts, this feature will be removed in a future
release of grep, and grep warns if it is used. Please use an
alias or script instead.
GREP_COLOR
This variable specifies the color used to highlight matched
(non-empty) text. It is deprecated in favor of GREP_COLORS,
but still supported. The mt, ms, and mc capabilities of
GREP_COLORS have priority over it. It can only specify the
color used to highlight the matching non-empty text in any
matching line (a selected line when the -v command-line option
is omitted, or a context line when -v is specified). The
default is 01;31, which means a bold red foreground text on
the terminal's default background.
GREP_COLORS
Specifies the colors and other attributes used to highlight
various parts of the output. Its value is a colon-separated
list of capabilities that defaults to
ms=01;31:mc=01;31:sl=:cx=:fn=35:ln=32:bn=32:se=36 with the rv
and ne boolean capabilities omitted (i.e., false). Supported
capabilities are as follows.
sl= SGR substring for whole selected lines (i.e., matching
lines when the -v command-line option is omitted, or
non-matching lines when -v is specified). If however
the boolean rv capability and the -v command-line
option are both specified, it applies to context
matching lines instead. The default is empty (i.e.,
the terminal's default color pair).
cx= SGR substring for whole context lines (i.e., non-
matching lines when the -v command-line option is
omitted, or matching lines when -v is specified). If
however the boolean rv capability and the -v command-
line option are both specified, it applies to selected
non-matching lines instead. The default is empty
(i.e., the terminal's default color pair).
rv Boolean value that reverses (swaps) the meanings of the
sl= and cx= capabilities when the -v command-line
option is specified. The default is false (i.e., the
capability is omitted).
mt=01;31
SGR substring for matching non-empty text in any
matching line (i.e., a selected line when the -v
command-line option is omitted, or a context line when
-v is specified). Setting this is equivalent to
setting both ms= and mc= at once to the same value.
The default is a bold red text foreground over the
current line background.
ms=01;31
SGR substring for matching non-empty text in a selected
line. (This is only used when the -v command-line
option is omitted.) The effect of the sl= (or cx= if
rv) capability remains active when this kicks in. The
default is a bold red text foreground over the current
line background.
mc=01;31
SGR substring for matching non-empty text in a context
line. (This is only used when the -v command-line
option is specified.) The effect of the cx= (or sl= if
rv) capability remains active when this kicks in. The
default is a bold red text foreground over the current
line background.
fn=35 SGR substring for file names prefixing any content
line. The default is a magenta text foreground over
the terminal's default background.
ln=32 SGR substring for line numbers prefixing any content
line. The default is a green text foreground over the
terminal's default background.
bn=32 SGR substring for byte offsets prefixing any content
line. The default is a green text foreground over the
terminal's default background.
se=36 SGR substring for separators that are inserted between
selected line fields (:), between context line fields,
(-), and between groups of adjacent lines when nonzero
context is specified (--). The default is a cyan text
foreground over the terminal's default background.
ne Boolean value that prevents clearing to the end of line
using Erase in Line (EL) to Right (\33[K) each time a
colorized item ends. This is needed on terminals on
which EL is not supported. It is otherwise useful on
terminals for which the back_color_erase (bce) boolean
terminfo capability does not apply, when the chosen
highlight colors do not affect the background, or when
EL is too slow or causes too much flicker. The default
is false (i.e., the capability is omitted).
Note that boolean capabilities have no =... part. They are
omitted (i.e., false) by default and become true when
specified.
See the Select Graphic Rendition (SGR) section in the
documentation of the text terminal that is used for permitted
values and their meaning as character attributes. These
substring values are integers in decimal representation and
can be concatenated with semicolons. grep takes care of
assembling the result into a complete SGR sequence (\33[...m).
Common values to concatenate include 1 for bold, 4 for
underline, 5 for blink, 7 for inverse, 39 for default
foreground color, 30 to 37 for foreground colors, 90 to 97 for
16-color mode foreground colors, 38;5;0 to 38;5;255 for
88-color and 256-color modes foreground colors, 49 for default
background color, 40 to 47 for background colors, 100 to 107
for 16-color mode background colors, and 48;5;0 to 48;5;255
for 88-color and 256-color modes background colors.
LC_ALL, LC_COLLATE, LANG
These variables specify the locale for the LC_COLLATE
category, which determines the collating sequence used to
interpret range expressions like [a-z].
LC_ALL, LC_CTYPE, LANG
These variables specify the locale for the LC_CTYPE category,
which determines the type of characters, e.g., which
characters are whitespace. This category also determines the
character encoding, that is, whether text is encoded in UTF-8,
ASCII, or some other encoding. In the C or POSIX locale, all
characters are encoded as a single byte and every byte is a
valid character.
LC_ALL, LC_MESSAGES, LANG
These variables specify the locale for the LC_MESSAGES
category, which determines the language that grep uses for
messages. The default C locale uses American English
messages.
POSIXLY_CORRECT
If set, grep behaves as POSIX requires; otherwise, grep
behaves more like other GNU programs. POSIX requires that
options that follow file names must be treated as file names;
by default, such options are permuted to the front of the
operand list and are treated as options. Also, POSIX requires
that unrecognized options be diagnosed as “illegal”, but since
they are not really against the law the default is to diagnose
them as “invalid”. POSIXLY_CORRECT also disables
_N_GNU_nonoption_argv_flags_, described below.
_N_GNU_nonoption_argv_flags_
(Here N is grep's numeric process ID.) If the ith character
of this environment variable's value is 1, do not consider the
ith operand of grep to be an option, even if it appears to be
one. A shell can put this variable in the environment for
each command it runs, specifying which operands are the
results of file name wildcard expansion and therefore should
not be treated as options. This behavior is available only
with the GNU C library, and only when POSIXLY_CORRECT is not
set.

Normally the exit status is 0 if a line is selected, 1 if no lines
were selected, and 2 if an error occurred. However, if the -q or
--quiet or --silent is used and a line is selected, the exit status
is 0 even if an error occurred.

Copyright 1998–2000, 2002, 2005–2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There
is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.

Reporting Bugs
Email bug reports to the bug-reporting address ⟨bug-grep@gnu.org⟩.
An email archive ⟨http://lists.gnu.org/mailman/listinfo/bug-grep⟩ and
a bug tracker ⟨http://debbugs.gnu.org/cgi/pkgreport.cgi?package=grep⟩
are available.
Known Bugs
Large repetition counts in the {n,m} construct may cause grep to use
lots of memory. In addition, certain other obscure regular
expressions require exponential time and space, and may cause grep to
run out of memory.
Back-references are very slow, and may require exponential time.

This page is part of the GNU grep (regular expression file search
tool) project. Information about the project can be found at
⟨https://www.gnu.org/software/grep/⟩. If you have a bug report for
this manual page, send it to bug-grep@gnu.org. This page was
obtained from the project's upstream Git repository
⟨git://git.savannah.gnu.org/grep.git⟩ on 2017-09-15. If you discover
any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page, or
you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a mail
to man-pages@man7.org
GNU grep 3.0.9-4f09-dirty 2017-06-21 GREP(1)